How to Make Spring Inject Value into a Static Field

Spring: How to inject a value to static field?

First of all, public static non-final fields are evil. Spring does not allow injecting to such fields for a reason.

Your workaround is valid, you don't even need getter/setter, private field is enough. On the other hand try this:

@Value("${my.name}")
public void setPrivateName(String privateName) {
    Sample.name = privateName;
}  

(works with @Autowired/@Resource). But to give you some constructive advice: Create a second class with private field and getter instead of public static field.

How to make spring inject value into a static field

You have two possibilities:

1. non-static setter for static property/field;
2. using org.springframework.beans.factory.config.MethodInvokingFactoryBean to invoke a static setter.

In the first option you have a bean with a regular setter but instead setting an instance property you set the static property/field.

public void setTheProperty(Object value) {
    foo.bar.Class.STATIC_VALUE = value;
}

but in order to do this you need to have an instance of a bean that will expose this setter (its more like an workaround).

In the second case it would be done as follows:

<bean class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
    <property name="staticMethod" value="foo.bar.Class.setTheProperty"/>
    <property name="arguments">
        <list>
            <ref bean="theProperty"/>
        </list>
   </property>
</bean>

On you case you will add a new setter on the Utils class:

public static setDataBaseAttr(Properties p)

and in your context you will configure it with the approach exemplified above, more or less like:

<bean class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
    <property name="staticMethod" value="foo.bar.Utils.setDataBaseAttr"/>
    <property name="arguments">
        <list>
            <ref bean="dataBaseAttr"/>
        </list>
   </property>
</bean>

How to inject property value using @Value into static fields

The only way is to use setter for this value

@Value("${value}")
public void setOutputPath(String outputPath) {
    AClass.outputPath = outputPath;
} 

However you should avoid doing this. Spring is not designed for static injections. Thus you should use another way to set this field at start of your application, e.g. constructor.
Anyway @Value annotation uses springs PropertyPlaceholder which is still resolved after static fields are initialized. Thus you won't have any advantages for this construction

How to assign a value from application.properties to a static variable?

Think about your problem for a second. You don't have to keep any properties from application.properties in static fields. The "workaround" suggested by Patrick is very dirty:

• you have no idea when this static field is modified
• you don't know which thread modifies it's value
• any thread at any time can change value of this static field and you are screwed
• initializing private static field that way has no sense to me

Keep in mind that when you have bean controlled by @Service annotation you delegate its creation to Spring container. Spring controls this bean lifecycle by creating only one bean that is shared across the whole application (of course you can change this behavior, but I refer to a default one here). In this case any static field has no sense - Spring makes sure that there is only one instance of UserService. And you get the error you have described, because static fields initialization happens many processor-cycles before Spring containers starts up. Here you can find more about when static fields are initialized.

Suggestion

It would be much better to do something like this:

@Service
public class UserService {
    private final String svnUrl;

    @Autowired
    public UserService(@Value("${SVN_URL}") String svnUrl) {
        this.svnUrl = svnUrl;
    }
}

This approach is better for a few reasons:

• constructor injection describes directly what values are needed to initialize the object
• final field means that this value wont be changed after it gets initialized in a constructor call (you are thread safe)

Using @ConfigurationProperties

There is also another way to load multiple properties to a single class. It requires using prefix for all values you want to load to your configuration class. Consider following example:

@ConfigurationProperties(prefix = "test")
public class TestProperties {

    private String svnUrl;

    private int somePort;

    // ... getters and setters
}

Spring will handle TestProperties class initialization (it will create a testProperties bean) and you can inject this object to any other bean initialized by Spring container. And here is what exemplary application.properties file look like:

test.svnUrl=https://svn.localhost.com/repo/
test.somePort=8080

Baeldung created a great post on this subject on his blog, I recommend reading it for more information.

Alternative solution

If you need somehow to use values in static context it's better to define some public class with public static final fields inside - those values will be instantiated when classloader loads this class and they wont be modified during application lifetime. The only problem is that you won't be able to load these values from Spring's application.properties file, you will have to maintain them directly in the code (or you could implement some class that loads values for these constants from properties file, but this sounds so verbose to the problem you are trying to solve).

Configure static field on boot with dependency injection Spring

You can't autowire static field directly, but you can set static field after application is initialized using @PostConstruct or catching ApplicationReadyEvent

public class MyApp {

    @Autowired
    TelegramBot telegramBot;

    @Autowired
    JavaMailSender javaMailSender

    @Value("${telegram-bot.default-chat}")
    String chatId;

    @Value("${mail.default-receiver}") 
    String to;

    @PostConstruct
    void setDefaults() {
        CustomerNotificationPreference.setDefaults(List.of(
            new TelegramNotificationChannel(telegramBot, chatId),
            new MailNotificationChannel(javaMailSender, to)
        ));
    }

    // OR

    @EventListener(ApplicationReadyEvent::class)
    void setDefaults() { 
        // same code as above
    }
    
} 

Make spring @Value take default value from static field

You may just want to inject Environment, and get the value as default like so:

@Configuration
public class MyConfiguration {

    public static final String DEFAULT_PROPERTY_VALUE = "long string...";

    @Autowired
    private Environment env;

    @Bean("midPriceDDSEndpoint")
    public DistributedDataSpace<Long, MidPriceStrategy> midPriceDDSEndpoint() {
        String myPropertyValue = env.getProperty("foo.bar.my-property", DEFAULT_PROPERTY_VALUE);
    }
}

I personally think that's a little bit more readable...

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